Overdose of acetaminophen (APAP), the popular analgesic and antipyretic agent, is the most common cause of acute liver failure (ALF) in the developing countries. Treatment options for APAP-induced ALF are extremely limited. Most ALF patients are treated with N-acetyl cystein, a precursor of glutathione, which works only if delivered within hours after APAP overdose. The only other therapy is liver transplantation, which is complicated by scarcity of donor organs, life long immunosuppressant use and exorbitant cost. There is a critical need to develop novel therapies for APAP-induced ALF. Recent studies in animal models and patients have demonstrated that timely stimulation of innate liver regeneration is associated with better outcomes including transplant free survival in APAP-induced ALF. These studies indicate that without proper liver regeneration APAP-induced acute liver injury can develop into ALF and result in death. Whereas these reports have underscored the therapeutic potential of liver regeneration following APAP-induced ALF, the mechanisms of liver regeneration after APAP overdose are not completely known. Our preliminary studies indicate that canonical Wnt signaling culminating in ?-catenin activation plays a critical role in liver regeneration after APAP- induced ALF and could be used for therapeutic targeting. The studies in the first specific aim will determine the role of each component of canonical Wnt pathway including ?-catenin, GSK3?, disheveled, Lrp5 and Wnt4 in liver regeneration after ALF. Another significant problem in developing regenerative therapies for ALF is the lack of reliable and easy to use biomarkers of liver regeneration. Currently, there are no reliable biomarkers that can be easily measured in serum of ALF patients, which can reveal the status of innate liver regeneration in ALF patients. Predictive models that factor in biomarkers of regeneration will allow clinicians to track status of patient's innate liver regeneration and aid in decisions on listing for transplantation. Our preliminary data indicate tha serum levels of leukocyte derived chemotaxin-2 (Lect2) could be used as a reliable biomarker of liver regeneration following acute liver failure. These studies will not only determine the role of Lect2 as a biomarker of regeneration in ALF but also determine role of Lect2 in stimulation of hepatocyte proliferation providing an additional therapeutic target. Overall, the studies in this grant proposal will determine the mechanisms of liver regeneration and identify novel biomarkers of liver regeneration specific to APAP-induced ALF. Successful completion of these studies will have substantial impact on clinical management of APAP-induced ALF patients.